Human energy needs amount to 17.75 trillion Joules every second; they are expected to at least double by 2050. In order to efficiently cover this steadily growing energy demand, all eyes are now turning to the sun: in one hour it emits more energy towards the earth than mankind needs in one year! This energy reserve has been largely untapped so far. Solar energy as we know it consists in converting sunlight into electricity, but researchers think they can also transform it into fuel.

Bio-mimicry: taking inspiration from and doing better than nature

Researchers at the JCAP (Joint Center for Artificial Photosynthesis) in Berkeley, California, are trying to replicate photosynthesis. This vegetal process allows any plant to use sunlight to split water molecules into oxygen (O2) and hydrogen atoms, also know as protons (H+). While oxygen is released into the atmosphere, the second step of the reaction combines protons (H+) into hydrogen atoms (H2), which in turn react with carbon dioxide (CO2) captured by the plant. While the final outcomes of the natural photosynthesis reaction are sugar and starch, the “artificial plants” researchers are working on could end up producing methanol or even fuel.

It took hundreds of millions of years for evolution to design this chain reaction underlying vegetal life. JCAP experts give themselves a couple of years to imitate and improve it. The chemical reaction they are working on should be ten times more efficient than natural photosynthesis. Research is so promising that the US Energy Department granted 122 million-dollar funding to the project. According to President Obama, this pioneering programme could eventually enable the US to become completely energy independent.

From hydrogen to liquid fuel

Daniel Nocera, chemist at the Massachusetts Institute of Technology (MIT), is also working on artificial photosynthesis. According to his estimates, a six by five-metre “solar foil” could cover the energy needs of a family home in four hours. His prototype uses sunlight to turn water into hydrogen (H2), which in turn can be used as fuel. Estimated costs are about three dollars per litre of hydrogen, which provides the same amount of energy as 3.75 litres of petrol.

Californian researchers are pursuing an even more ambitious goal: producing liquid fuel which could then be processed in a refinery to fill our car’s tank, just like petrol, which is much better than highly explosive hydrogen gas.

Paradigm shift in our vision of renewable energy

Solar energy as we know it today comes from solar panels or concentrating solar power (CSP) schemes. Both are examples of photovoltaic energy, since light (photo-) is turned into electricity (Volts). The major drawback of solar power is that it is still impossible to store it in bulk and to transport it without significant losses. Directly turning solar energy into fuel on a big scale could lead us to rethink our conception of renewable energy as a whole. Electricity could then cease to be the only environment-friendly sustainable energy to be produced from a renewable source.